1. Field of the Invention
This invention relates to a blood reservoir or a hollow fibre type oxygenator in which the blood flow channel section of the blood reservoir or at least a fraction of the outer wall surfaces of the hollow fibre of the oxygenator is subjected to a chemical treatment such as with acid or albumin solutions or polyhydroxyethyl methacrylate, hereafter referred to as PHEMA, discharge treatment such as by corona or plasma treatment or with ozone and thereby hydrophilized to improve wettability thereof with the blood.
This invention also relates to medical implements or instruments in which the blood flow channel sections are hydrophilizingly treated using a polymer such as hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) of using poly(oxyethylene)-poly(oxypropylene) block polymer after treated using above polymer.
2. Prior Art
Various polymers employed in the materials of medical implements are generally of hydrophobic properties. However, depending on usage and applications, not few of these materials require a hydrophilizing surface treatment.
In an oxygenator, for example, the housing is divided by a gas exchange membrane into two sections and a gas exchange is effected between the blood flowing in one of these sections and the gas, mostly oxygen, flowing in the other section. As a gas exchange membrane, polypropylene, polystyrene or silicone membranes, exhibiting hydrophobic properties, are frequently employed.
It is noted that, before using the oxygenator, a priming operation is usually carried out to remove the air contained in the oxygenator. The membrane is hydrophobic and exhibits only poor affinity with water so that the air cannot be eliminated completely in the course of the priming operation. Above all, in the case of a hollow fibre type oxygenator employing porous hollow fibre as the gas exchange membrane, with the blood being caused to flow outside of the hollow fibre, there is demonstrated a strong tendency for the air to become trapped between the adjacent fibers of the hollow fibre. The result is that these adjacent fibers become flocculated by the air to form so-called cavities to lower the gas exchange performance.
The majority of the hollow fibre type oxygenators hitherto evolved were of the type in which the blood is caused to flow within the inside of the hollow fibre. However, because of large pressure losses encountered, it is felt that this type of the oxygenator can be applied to pulsed flow excorporeal circulation, separate excorporeal circulation or blood cardioplegia, only with considerable difficulties.
When the blood and the gas are caused to flow outside and inside of the hollow fibre, respectively, pressure losses may be lowered, so that the blood can be supplied to the oxygenator and thence to the blood reservoir by blood movement caused only by the pressure head from the patient's body without the necessity of providing a blood delivery pump ahead of the oxygenator in the circulating circuit. In this manner, the oxygenator can be adapted to blood cardioplegia or to separate excorporeal circulation.
With the hollow fibre formed by a hydrophobic resin, the fibre surface exhibits only low wettability by the blood, so that the blood cannot be distributed satisfactorily between the adjacent hollow fibre. Hence an effective gas exchange via the hollow fibre is obstructed and a sufficient gas exchange performance is not achieved. For wetting the outer wall surfaces of the hollow fibre, the air bubbles remaining between the hollow fibre need be removed by imparting as physical shock, such as by a laborious operation of striking the oxygenator.
In open heart surgery, a blood circuit with a built-in oxygenator is used in place of the living lung to eliminate carbon dioxide in the blood and to replenish oxygen in excorporeal circulation.
In the excorporeal blood circulation circuit with the built-in oxygenator, a blood reservoir is provided to eliminate air bubbles occasionally flowing int the circuit or to store and replenish the blood in the event of possible decrease in the blood circulation caused by, for example, tube rupture in the circuit.
In view of relative ease with which the stored blood quantity can be ascertained and the blood of a large volume can be stored, a hard shell type blood reservoir, formed of a hard material, is generally employed. Since the blood reservoir can then be incorporated easily into the oxygenator, there is proposed an oxygenator with a build-in blood reservoir.
However, when the blood reservoir exhibits hydrophobic properties, the blood or the priming liquid is not allowed to flow uniformly on the overall surface of the blood flow channel, but flows as a partialized flow into the blood reservoir to produce air bubbles.
The hard shell type blood reservoir 1 integrated to the oxygenator is shown diagrammatically in FIG. 1 and formed by a housing 7 formed of a hard material and including a blood inlet port 2, a blood influent section 5 communicating with the inlet port and presenting a bottom surface having substantially no drop from the inlet port 2, a blood reservoir section 6 communicating with the blood influent section and presenting a bottom surface gradually descending from the section 5 and a blood outlet 3 formed at the bottom of the reservoir section 6. It is noted that the bottom surfaces of the blood influent section 5 and the blood reservoir section 6 and the lateral sides of the housing 7 represent a blood flow channel surface.
The blood introduced via the blood inlet port 2 is caused to flow on the blood flow channel surface 4 so as to descend to and be stored in the blood storage section 6.
Heretofore, the housing 7 of the blood reservoir 1 was formed by a member of a material exhibiting hydrophobic properties, such as, for example, hard vinyl chloride resin, styrene resin or carbonate resin. As a result, the blood flow channel surface 4 also exhibited hydrophobic properties, so that, on performing bloodless priming, the priming liquid will flow as a partialized flow without flowing uniformly on the overall blood flow channel surface 4. In this manner, the liquid flow will be disturbed and the priming liquid flows into the blood storage section 6 just like a fall flows down into a pond to produce the air bubbles or foam in the blood storage section 6. In addition, the above materials are not said to be satisfactory in compatibility to the blood.
It will be noted that the filter medium for removal of foreign matter of a blood filter or arterial filter provided downstream of the excorporeal circulating circuit is in the form of pleats, for elevating the properties of removal of foreign matter, s that air bubbles cannot be removed easily. Also, since the materials are hydrophobic, they are low in wettability, so that a certain pressure head is necessitated in the priming operation, which renders the priming operation difficult.
For combatting the above deficiency and improving wettability of the blood flow channel surface by the blood or the priming liquid, attempts have been made to hydrolyze the blood flow channel surface by a suitable surface treatment. However, these attempts have not met with success because of difficulties in simultaneously achieving uniform hydrophilic properties and improved compatibility to the blood without changing the properties of the material.
It is therefore an object of the present invention to provide an oxygenator in which the outer wall surface of the hollow fibre is hydrophilized to improve wettability thereof by the blood and the priming liquid to suppress formation of air bubbles without lowering the gas exchange properties.
It is another object of the present invention to provide a blood reservoir in which the blood flow channel surface is hydrophilized in part or in its entirety to improve wettability thereof by the blood and the priming liquid to suppress generation of air bubbles or foam by the blood flowing into the blood storage section.
The present invention has been fulfilled as a result of out perseverant researches for combatting the above deficiencies mainly caused by the hydrophobic properties of the blood flow channel sections of the medical instruments. It is an object of the present invention to provide a medical instrument in which at least the blood flow channel section thereof is subjected to a hydrophilizing treatment to improve wettability thereof by the blood or by the priming liquid to prevent affixture of air bubbles while simultaneously improving compatibility to the blood of the medical instrument.
The present invention has been fulfilled as a result of our perseverant researche for eliminating the above deficiencies mainly caused by the hydrophobic properties of the blood flow channel sections of the medical instrument. It is another object of the present invention to provide a medical instrument in which at least the blood flow channel section thereof is subjected to a hydrophilizing treatment to improve wettability thereof by the blood or by the priming liquid while simultaneously improving compatibility to the blood of the medical instrument.